Implantable medical devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable device is an implantable cardioverter-defibrillator (ICD), a pacemaker, or a combination thereof, having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such a device commonly includes a hermetically sealed case or housing within which a power supply and control circuitry are placed. Additionally, one or more conductive leads will typically extend from the housing to a selected muscle structure within a patient.
Recently, there is the desire to chronically implant more physiological sensors within a patient to monitor various hemodynamic functions of the patient. If the patient already requires an implantable device, such as an ICD or pacemaker (referred to collectively hereafter as an implantable stimulation device), it is preferably to integrate any additional physiological sensors into the implantable stimulation device, so as to minimize the number of implants. Such sensors can include, for example, optoelectronic sensors that are useful for producing photoplethysmography signals and for obtaining measures of oxygen saturation using pulse oximetry. Other types of sensors include, but are not limited to, acoustic sensors that can measure heart sounds, temperature transducers, impedance sensors, electro-chemical sensors and ultrasound transducers.
Integrating additional sensing hardware into an implantable device increases the development and regulatory costs of the device. For can-based devices, such as ICDs and pacemakers, some of this cost is due to the need to redesign the layout of the internal components in order to accommodate the volume occupied by the additional sensor hardware. Additionally, providing signal connections, data management, and telemetry requires changes to device electronics, software and/or firmware. There are also additional burdens to Quality Assurance to verify that the additional sensor hardware does not compromise the conventional functions of the implantable device. For example, the power requirements of the sensor hardware may be such that it reduces the battery life of an ICD to an unacceptable level.
It would be desirable if additional sensing hardware can be integrated into implantable devices more quickly and less expensively. Further, it would be desirable if the affects on the conventional functions of implantable devices are reduced, and preferably minimized.